Addressing letters when two people with different last names live at same address

I'm using Word 2003 and trying to set up a letter using mail merge. I
am having trouble making it work when I need to send the letter to two
people with different surnames living at the same address. I have
managed to set up the address line of the document as follows:

{ MERGEFIELD Title \f " " }{ MERGEFIELD First_name \f " " }{ MERGEFIELD
"Surname" \f " " }{ IF { MERGEFIELD M_2nd_Surname} "" "& " "" }{
MERGEFIELD "M_2nd_Forename" \f " " }{ MERGEFIELD "M_2nd_Surname" \f " "
}

However, I am having difficulty with the greeting line of the document,
I want it to be able to figure out the following:

If both names have title information available, then use Dear Mr. Jones
and Ms. Smith
If there is only one person, and we know their title, it should just
say Dear Mr. Jones
In all other cases, it should say Dear Sir/Madam

Please can anyone help?

Many thanks,
Naomi




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madrayakin